// SPDX-License-Identifier: MIT
// File: StableCoin_flat.sol


// File: @openzeppelin/contracts/utils/math/SafeMath.sol


// OpenZeppelin Contracts v4.4.1 (utils/math/SafeMath.sol)

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is generally not needed starting with Solidity 0.8, since the compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol


// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: @openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol


// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

pragma solidity ^0.8.0;


/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}

// File: @openzeppelin/contracts/utils/introspection/IERC165.sol


// OpenZeppelin Contracts v4.4.1 (utils/introspection/IERC165.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

// File: @openzeppelin/contracts/utils/introspection/ERC165.sol


// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)

pragma solidity ^0.8.0;


/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
 * for the additional interface id that will be supported. For example:
 *
 * ```solidity
 * function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
 *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
 * }
 * ```
 *
 * Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
 */
abstract contract ERC165 is IERC165 {
    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IERC165).interfaceId;
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol


// OpenZeppelin Contracts v4.4.1 (utils/Strings.sol)

pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }
}

// File: @openzeppelin/contracts/access/IAccessControl.sol


// OpenZeppelin Contracts v4.4.1 (access/IAccessControl.sol)

pragma solidity ^0.8.0;

/**
 * @dev External interface of AccessControl declared to support ERC165 detection.
 */
interface IAccessControl {
    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
     *
     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call, an admin role
     * bearer except when using {AccessControl-_setupRole}.
     */
    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Emitted when `account` is revoked `role`.
     *
     * `sender` is the account that originated the contract call:
     *   - if using `revokeRole`, it is the admin role bearer
     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
     */
    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) external view returns (bool);

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {AccessControl-_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) external view returns (bytes32);

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) external;

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) external;

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) external;
}

// File: @openzeppelin/contracts/utils/Context.sol


// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// File: contracts/Ownable.sol


pragma solidity ^0.8.0;


contract Ownable is Context {
    address private _owner;
    address private _proposedOwner;

    event ProposeOwner(address indexed proposedOwner);
    event ClaimOwnership(address newOwner);

    constructor() {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit ClaimOwnership(msgSender);
    }

    function owner() public view returns (address) {
        return _owner;
    }

    function proposedOwner() public view returns (address) {
        return _proposedOwner;
    }

    modifier onlyOwner() {
        require(
            _owner == _msgSender(),
            "Only the owner can call this function."
        );
        _;
    }

    modifier onlyProposedOwner() {
        require(
            _msgSender() == _proposedOwner,
            "Only the proposed owner can call this function."
        );
        _;
    }

    function disregardProposedOwner() private onlyOwner {
        _proposedOwner = address(0);
    }

    function proposeOwner(address newOwner) public onlyOwner {
        require(newOwner != address(0), "Cannot propose 0x0 as new owner.");
        _proposedOwner = newOwner;
        emit ProposeOwner(_proposedOwner);
    }

    function claimOwnership() public virtual onlyProposedOwner {
        _owner = _proposedOwner;
        _proposedOwner = address(0);
        emit ClaimOwnership(_owner);
    }

    uint256[49] private __gap;
}
// File: contracts/ExternallyTransferable.sol


pragma solidity ^0.8.0;



abstract contract ExternallyTransferable is Context {
    using SafeMath for uint256;

    // address => string (network URI) => bytes (external address) => amount
    mapping(address => mapping(string => mapping(bytes => uint256)))
        private _externalAllowances;

    function externalAllowanceOf(
        address owner,
        string memory networkURI,
        bytes memory externalAddress
    ) public view returns (uint256) {
        return _externalAllowances[owner][networkURI][externalAddress];
    }

    // User calls to allocate external transfer
    function approveExternalTransfer(
        string memory networkURI,
        bytes memory externalAddress,
        uint256 amount
    ) public virtual {
        _approveExternalAllowance(_msgSender(), networkURI, externalAddress, amount);
    }

    // Bridge calls after externalTransfer
    function _approveExternalAllowance(
        address from,
        string memory networkURI,
        bytes memory to,
        uint256 amount
    ) internal virtual {
        require(_msgSender() != address(0), "Approve from the zero address");
        require(from != address(0), "Approve for the zero address");
        _externalAllowances[from][networkURI][to] = amount;
    }

    // Bridge calls to burn coins on this network (sending external transfer)
    function externalTransfer(
        address from,
        string memory networkURI,
        bytes memory to, // external address
        uint256 amount
    ) public virtual {}

    // Bridge calls to mint coins on this network (receiving external transfer)
    function externalTransferFrom(
        bytes memory from, // external address
        string memory networkURI,
        address to,
        uint256 amount
    ) public virtual {}
}
// File: @openzeppelin/contracts/token/ERC20/ERC20.sol


// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC20/ERC20.sol)

pragma solidity ^0.8.0;




/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin Contracts guidelines: functions revert
 * instead returning `false` on failure. This behavior is nonetheless
 * conventional and does not conflict with the expectations of ERC20
 * applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

    mapping(address => mapping(address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * The default value of {decimals} is 18. To select a different value for
     * {decimals} you should overload it.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5.05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless this function is
     * overridden;
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual override returns (uint8) {
        return 18;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address to, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, amount);
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        address owner = _msgSender();
        _approve(owner, spender, _allowances[owner][spender] + addedValue);
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        address owner = _msgSender();
        uint256 currentAllowance = _allowances[owner][spender];
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `sender` to `recipient`.
     *
     * This internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     */
    function _transfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(from, to, amount);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - amount;
        }
        _balances[to] += amount;

        _afterTokenTransfer(from, to, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply += amount;
        _balances[account] += amount;
        emit Transfer(address(0), account, amount);

        _afterTokenTransfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        unchecked {
            _balances[account] = accountBalance - amount;
        }
        _totalSupply -= amount;

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Spend `amount` form the allowance of `owner` toward `spender`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    function _spendAllowance(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - amount);
            }
        }
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * has been transferred to `to`.
     * - when `from` is zero, `amount` tokens have been minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens have been burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _afterTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}
}

// File: @openzeppelin/contracts/access/AccessControl.sol


// OpenZeppelin Contracts (last updated v4.5.0) (access/AccessControl.sol)

pragma solidity ^0.8.0;





/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms. This is a lightweight version that doesn't allow enumerating role
 * members except through off-chain means by accessing the contract event logs. Some
 * applications may benefit from on-chain enumerability, for those cases see
 * {AccessControlEnumerable}.
 *
 * Roles are referred to by their `bytes32` identifier. These should be exposed
 * in the external API and be unique. The best way to achieve this is by
 * using `public constant` hash digests:
 *
 * ```
 * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
 * ```
 *
 * Roles can be used to represent a set of permissions. To restrict access to a
 * function call, use {hasRole}:
 *
 * ```
 * function foo() public {
 *     require(hasRole(MY_ROLE, msg.sender));
 *     ...
 * }
 * ```
 *
 * Roles can be granted and revoked dynamically via the {grantRole} and
 * {revokeRole} functions. Each role has an associated admin role, and only
 * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
 *
 * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
 * that only accounts with this role will be able to grant or revoke other
 * roles. More complex role relationships can be created by using
 * {_setRoleAdmin}.
 *
 * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
 * grant and revoke this role. Extra precautions should be taken to secure
 * accounts that have been granted it.
 */
abstract contract AccessControl is Context, IAccessControl, ERC165 {
    struct RoleData {
        mapping(address => bool) members;
        bytes32 adminRole;
    }

    mapping(bytes32 => RoleData) private _roles;

    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

    /**
     * @dev Modifier that checks that an account has a specific role. Reverts
     * with a standardized message including the required role.
     *
     * The format of the revert reason is given by the following regular expression:
     *
     *  /^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/
     *
     * _Available since v4.1._
     */
    modifier onlyRole(bytes32 role) {
        _checkRole(role, _msgSender());
        _;
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IAccessControl).interfaceId || super.supportsInterface(interfaceId);
    }

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) public view virtual override returns (bool) {
        return _roles[role].members[account];
    }

    /**
     * @dev Revert with a standard message if `account` is missing `role`.
     *
     * The format of the revert reason is given by the following regular expression:
     *
     *  /^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/
     */
    function _checkRole(bytes32 role, address account) internal view virtual {
        if (!hasRole(role, account)) {
            revert(
                string(
                    abi.encodePacked(
                        "AccessControl: account ",
                        Strings.toHexString(uint160(account), 20),
                        " is missing role ",
                        Strings.toHexString(uint256(role), 32)
                    )
                )
            );
        }
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) public view virtual override returns (bytes32) {
        return _roles[role].adminRole;
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) public virtual override onlyRole(getRoleAdmin(role)) {
        _grantRole(role, account);
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) public virtual override onlyRole(getRoleAdmin(role)) {
        _revokeRole(role, account);
    }

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been revoked `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) public virtual override {
        require(account == _msgSender(), "AccessControl: can only renounce roles for self");

        _revokeRole(role, account);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event. Note that unlike {grantRole}, this function doesn't perform any
     * checks on the calling account.
     *
     * [WARNING]
     * ====
     * This function should only be called from the constructor when setting
     * up the initial roles for the system.
     *
     * Using this function in any other way is effectively circumventing the admin
     * system imposed by {AccessControl}.
     * ====
     *
     * NOTE: This function is deprecated in favor of {_grantRole}.
     */
    function _setupRole(bytes32 role, address account) internal virtual {
        _grantRole(role, account);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.
     *
     * Emits a {RoleAdminChanged} event.
     */
    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
        bytes32 previousAdminRole = getRoleAdmin(role);
        _roles[role].adminRole = adminRole;
        emit RoleAdminChanged(role, previousAdminRole, adminRole);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * Internal function without access restriction.
     */
    function _grantRole(bytes32 role, address account) internal virtual {
        if (!hasRole(role, account)) {
            _roles[role].members[account] = true;
            emit RoleGranted(role, account, _msgSender());
        }
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * Internal function without access restriction.
     */
    function _revokeRole(bytes32 role, address account) internal virtual {
        if (hasRole(role, account)) {
            _roles[role].members[account] = false;
            emit RoleRevoked(role, account, _msgSender());
        }
    }
}

// File: @openzeppelin/contracts/security/Pausable.sol


// OpenZeppelin Contracts v4.4.1 (security/Pausable.sol)

pragma solidity ^0.8.0;


/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor() {
        _paused = false;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        require(!paused(), "Pausable: paused");
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        require(paused(), "Pausable: not paused");
        _;
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

// File: contracts/StableCoin.sol


pragma solidity ^0.8.0;

contract StableCoin is
    Context, // provides _msgSender(), _msgData()
    Pausable, // provides _pause(), _unpause()
    Ownable, // Ownable, Claimable
    AccessControl, // RBAC for KYC, Frozen
    ERC20, // ERC20 Functions (transfer, balance, allowance, mint, burn)
    ExternallyTransferable // Supports External Transfers
{
    using SafeMath for uint256;
    //using SafeERC20 for IERC20;

    // Defined Roles
    bytes32 private constant KYC_PASSED = keccak256("KYC_PASSED");
    bytes32 private constant FROZEN = keccak256("FROZEN");

    // Special People
    address private _supplyManager;
    address private _complianceManager;
    address private _enforcementManager;

    // Events Emitted
    event Constructed(
        string tokenName,
        string tokenSymbol,
        uint256 totalSupply
    );

    // Privileged Roles
    event ChangeSupplyManager(address newSupplyManager);
    event ChangeComplianceManager(address newComplianceManager);
    event ChangeEnforcementManager(address newEnforcementManager);

    // ERC20+
    event Wipe(address account, uint256 amount);
    event Mint(address account, uint256 amount);
    event Burn(address account, uint256 amount);
    //event Transfer(address sender, address recipient, uint256 amount);
    event Approve(address sender, address spender, uint256 amount);
    event IncreaseAllowance(address sender, address spender, uint256 amount);
    event DecreaseAllowance(address sender, address spender, uint256 amount);

    // KYC
    event Freeze(address account); // Freeze: Freeze this account
    event Unfreeze(address account);
    event SetKycPassed(address account);
    event UnsetKycPassed(address account);

    // Halt
    event Pause(address sender); // Pause: Pause entire contract
    event Unpause(address sender);

    // "External Transfer"
    // Signify to the coin bridge to perform external transfer
    event ApproveExternalTransfer(address from,string networkURI,bytes to,uint256 amount);
    event ExternalTransfer(address from,string networkURI,bytes to,uint256 amount);
    event ExternalTransferFrom(bytes from,string networkURI,address to,uint256 amount);

    constructor() ERC20("Gram Gold", "GRAMG") {
        _supplyManager = _msgSender();
        _complianceManager = _msgSender();
        _enforcementManager = _msgSender();

        // Owner has Admin Privileges on all roles
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender()); // sudo role

        // Give CM ability to grant/revoke roles (but not admin of this role)
        grantRole(DEFAULT_ADMIN_ROLE, _msgSender());

        // KYC accounts
        grantRole(KYC_PASSED, _msgSender());
        grantRole(KYC_PASSED, _msgSender());
        grantRole(KYC_PASSED, _msgSender());
        grantRole(KYC_PASSED, _msgSender());

        // Give supply manager all tokens
        mint(0); // Emits Mint

        
        // Did it
        emit Constructed(
            name(),
            symbol(),
            0
        );
    }

    /*
     * RBAC
     */

    function supplyManager() public view returns (address) {
        return _supplyManager;
    }

    modifier onlySupplyManager() {
        require(
            _msgSender() == supplyManager() || _msgSender() == owner(),
            "Only the supply manager can call this function."
        );
        _;
    }

    function changeSupplyManager(address newSupplyManager) public onlyOwner {
        require(
            newSupplyManager != address(0),
            "Cannot change supply manager to 0x0."
        );
        revokeRole(KYC_PASSED, _supplyManager);
        _supplyManager = newSupplyManager;
        grantRole(KYC_PASSED, _supplyManager);
        revokeRole(FROZEN, _supplyManager);
        emit ChangeSupplyManager(newSupplyManager);
    }

    function complianceManager() public view returns (address) {
        return _complianceManager;
    }

    modifier onlyComplianceManager() {
        require(
            _msgSender() == complianceManager() || _msgSender() == owner(),
            "Only the Compliance Manager can call this function."
        );
        _;
    }

    function changeComplianceManager(address newComplianceManager)
        public
        onlyOwner
    {
        require(
            newComplianceManager != address(0),
            "Cannot change compliance manager to 0x0."
        );
        revokeRole(KYC_PASSED, _complianceManager);
        _complianceManager = newComplianceManager;
        grantRole(KYC_PASSED, _complianceManager);
        revokeRole(FROZEN, _complianceManager);
        emit ChangeComplianceManager(newComplianceManager);
    }

    function enforcementManager() public view returns (address) {
        return _enforcementManager;
    }

    modifier onlyEnforcementManager() {
        require(
            _msgSender() == enforcementManager() || _msgSender() == owner(),
            "Only the Enforcement Manager can call this function."
        );
        _;
    }

    function changeEnforcementManager(address newEnforcementManager)
        public
        onlyOwner
    {
        require(
            newEnforcementManager != address(0),
            "Cannot change enforcement manager to 0x0"
        );
        revokeRole(KYC_PASSED, _enforcementManager);
        _enforcementManager = newEnforcementManager;
        grantRole(KYC_PASSED, _enforcementManager);
        revokeRole(FROZEN, _enforcementManager);
        emit ChangeEnforcementManager(newEnforcementManager);
    }

    function isPrivilegedRole(address account) public view returns (bool) {
        return
            account == supplyManager() ||
            account == complianceManager() ||
            account == enforcementManager() ||
            account == owner();
    }

    modifier requiresKYC() {
        require(
            hasRole(KYC_PASSED, _msgSender()),
            "Calling this function requires KYC approval."
        );
        _;
    }

    function isKycPassed(address account) public view returns (bool) {
        return hasRole(KYC_PASSED, account);
    }

    // KYC: only CM
    function setKycPassed(address account) public onlyComplianceManager {
        grantRole(KYC_PASSED, account);
        emit SetKycPassed(account);
    }

    // Un-KYC: only CM, only non-privileged accounts
    function unsetKycPassed(address account) public onlyComplianceManager {
        require(
            !isPrivilegedRole(account),
            "Cannot unset KYC for administrator account."
        );
        require(account != address(0), "Cannot unset KYC for address 0x0.");
        revokeRole(KYC_PASSED, account);
        emit UnsetKycPassed(account);
    }

    modifier requiresNotFrozen() {
        require(
            !hasRole(FROZEN, _msgSender()),
            "Your account has been frozen, cannot call function."
        );
        _;
    }

    function isFrozen(address account) public view returns (bool) {
        return hasRole(FROZEN, account);
    }

    // Freeze an account: only CM, only non-privileged accounts
    function freeze(address account) public onlyComplianceManager {
        require(
            !isPrivilegedRole(account),
            "Cannot freeze administrator account."
        );
        require(account != address(0), "Cannot freeze address 0x0.");
        grantRole(FROZEN, account);
        emit Freeze(account);
    }

    // Unfreeze an account: only CM
    function unfreeze(address account) public onlyComplianceManager {
        revokeRole(FROZEN, account);
        emit Unfreeze(account);
    }

    // Check Transfer Allowed (user facing)
    function checkTransferAllowed(address account) public view returns (bool) {
        return isKycPassed(account) && !isFrozen(account);
    }

    // Pause: Only CM
    function pause() public onlyComplianceManager {
        _pause();
        emit Pause(_msgSender());
    }

    // Unpause: Only CM
    function unpause() public onlyComplianceManager {
        _unpause();
        emit Unpause(_msgSender());
    }

    // Claim Ownership
    function claimOwnership() public override(Ownable) onlyProposedOwner {
        address prevOwner = owner();
        super.claimOwnership(); // emits ClaimOwnership
        _setupRole(DEFAULT_ADMIN_ROLE, _msgSender());
        grantRole(KYC_PASSED, _msgSender());
        revokeRole(FROZEN, _msgSender());
        revokeRole(KYC_PASSED, prevOwner);
    }

    // Wipe
    function wipe(address account, uint256 amount) public onlyEnforcementManager {
        uint256 balance = balanceOf(account);
        require(
            amount <= balance,
            "Amount cannot be greater than balance"
        );
        super._transfer(account, _supplyManager, amount);
        _burn(_supplyManager, amount);
        emit Wipe(account, amount);
    }

    /*
     * Transfers
     */

    // Mint
    function mint(uint256 amount) public onlySupplyManager {
        _mint(supplyManager(), amount * 10 ** decimals());
        emit Mint(_msgSender(), amount );
    }

    // Burn
    function burn(uint256 amount) public onlySupplyManager {
        _burn(_supplyManager, amount * 10 ** decimals());
        emit Burn(_msgSender(), amount);
    }

    // Check Transfer Allowed (internal)
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal override(ERC20) requiresNotFrozen whenNotPaused {
        if (from == supplyManager() && to == address(0)) {
            // allowed (burn)
            super._beforeTokenTransfer(from, to, amount);
            return;
        }

        if (to == supplyManager() && from == address(0)) {
            // allowed (mint)
            super._beforeTokenTransfer(from, to, amount);
            return;
        }

        if (
            to == supplyManager() &&
            hasRole(FROZEN, from) &&
            amount == balanceOf(from)
        ) {
            // allowed (wipe account)
            super._beforeTokenTransfer(from, to, amount);
            return;
        }

        // All other transfers
        //require(isKycPassed(from), "Sender account requires KYC to continue.");
        //require(isKycPassed(to), "Receiver account requires KYC to continue.");
        require(!isFrozen(from), "Sender account is frozen.");
        require(!isFrozen(to), "Receiver account is frozen.");
        super._beforeTokenTransfer(from, to, amount); // callbacks from above (if any)
    }

    function transfer(address to, uint256 amount) public override(ERC20) returns (bool) {
        super._transfer(_msgSender(), to, amount);
        emit Transfer(_msgSender(), to, amount);
        return  true;
    }

    /*
     * External Transfers
     */

    // approve an allowance for transfer to an external network
    function approveExternalTransfer(
        string memory networkURI,
        bytes memory externalAddress,
        uint256 amount
    )
        public
        override(ExternallyTransferable)
        requiresKYC
        requiresNotFrozen
        whenNotPaused
    {
        require(
            amount <= balanceOf(_msgSender()),
            "Cannot approve more than balance."
        );
        super.approveExternalTransfer(networkURI, externalAddress, amount);
        emit ApproveExternalTransfer(
            _msgSender(),
            networkURI,
            externalAddress,
            amount
        );
    }

    function externalTransfer(
        address from,
        string memory networkURI,
        bytes memory to,
        uint256 amount
    ) public override(ExternallyTransferable) onlySupplyManager whenNotPaused {
        require(isKycPassed(from), "Spender account requires KYC to continue.");
        require(!isFrozen(from), "Spender account is frozen.");
        uint256 exAllowance = externalAllowanceOf(from, networkURI, to);
        require(amount <= exAllowance, "Amount greater than allowance.");
        super._transfer(from, _supplyManager, amount);
        _burn(_supplyManager, amount);
        _approveExternalAllowance(
            from,
            networkURI,
            to,
            exAllowance.sub(amount)
        );
        emit ExternalTransfer(from, networkURI, to, amount);
    }

    function externalTransferFrom(
        bytes memory from,
        string memory networkURI,
        address to,
        uint256 amount
    ) public override(ExternallyTransferable) onlySupplyManager whenNotPaused {
        require(isKycPassed(to), "Recipient account requires KYC to continue.");
        require(!isFrozen(to), "Recipient account is frozen.");
        _mint(_supplyManager, amount);
        super._transfer(_supplyManager, to, amount);
        emit ExternalTransferFrom(from, networkURI, to, amount);
    }

    /*
     * Allowances
     */

    // Check Allowance Allowed (internal)
    function _beforeTokenAllowance(
        address sender,
        address spender,
        uint256 amount
    ) internal requiresKYC requiresNotFrozen whenNotPaused view {
        require(isKycPassed(spender), "Spender account requires KYC to continue.");
        require(isKycPassed(sender), "Sender account requires KYC to continue.");
        require(!isFrozen(spender), "Spender account is frozen.");
        require(!isFrozen(sender), "Sender account is frozen.");
        require(amount >= 0, "Allowance must be greater than 0.");
    }

    // Transfer From (allowance --> user)
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public override requiresKYC requiresNotFrozen returns (bool){
        bool returnValue = super.transferFrom(from, to, amount);
        emit Transfer(from, to, amount);
        emit Approve(from, _msgSender(), allowance(from, _msgSender()));
        return returnValue;
    }

    // Approve Allowance
    function approveAllowance(address spender, uint256 amount)
        public
        requiresKYC
        requiresNotFrozen
    {
        _beforeTokenAllowance(_msgSender(), spender, amount);
        super._approve(_msgSender(), spender, amount);
        emit Approve(_msgSender(), spender, amount);
    }

    // Increase Allowance
    function increaseAllowance(address spender, uint256 amount)
        public
        override(ERC20)
        requiresKYC
        requiresNotFrozen
        returns (bool)
    {
        uint256 newAllowance = allowance(_msgSender(), spender).add(amount);
        _approve(_msgSender(), spender, newAllowance);
        emit IncreaseAllowance(_msgSender(), spender, newAllowance);
        return true;
    }

    // Decrease Allowance
    function decreaseAllowance(address spender, uint256 amount)
        public
        override(ERC20)
        requiresKYC
        requiresNotFrozen
        returns (bool)
    {
        uint256 newAllowance = allowance(_msgSender(), spender).sub(
            amount,
            "Amount greater than allowance."
        );
        _approve(_msgSender(), spender, newAllowance);
        emit DecreaseAllowance(_msgSender(), spender, newAllowance);
        return true;
    }
}

{
  "compilationTarget": {
    "StableCoin.sol": "StableCoin"
  },
  "evmVersion": "london",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}